A Keychain Wrapper for String Key and Value to save sensitive data in Apple Keychain

KeychainWrapper.swift

import Foundation
import Security

public enum KeychainWrapperError: Error {
    case emptyKeyOrValue
    case failure(status: OSStatus)
}

class KeychainWrapper {
    
    public func set(string: String, forKey key: String) throws {
        guard !string.isEmpty && !key.isEmpty else {
            throw KeychainWrapperError.emptyKeyOrValue
        }
        
        do{
            try removeString(forKey: key)
        } catch {
            throw error
        }
        
        var qd = setupQueryDictionary(forKey: key)
        qd[kSecValueData as String] = string.data(using: .utf8)
        
        let status = SecItemAdd(qd as CFDictionary, nil)
        
        if status != errSecSuccess {
            throw KeychainWrapperError.failure(status: status)
        }
    }
    
    public func get(forKey key: String) throws -> String? {
        guard !key.isEmpty else {
            throw KeychainWrapperError.emptyKeyOrValue
        }
        
        var qd = setupQueryDictionary(forKey: key)
        qd[kSecReturnData as String] = kCFBooleanTrue
        qd[kSecMatchLimit as String] = kSecMatchLimitOne
        
        var data: AnyObject?
        let status = SecItemCopyMatching(qd as CFDictionary, &data)
        
        if status != errSecSuccess {
            throw KeychainWrapperError.failure(status: status)
        }
        
        let result: String?
        if (data as? Data) != nil {
            result = String(data: data as! Data, encoding: .utf8)
        } else {
            result = nil
        }
        return result
    }
    
    public func removeString(forKey key: String) throws  {
        guard !key.isEmpty else {
            throw KeychainWrapperError.emptyKeyOrValue
        }
        
        let qd = setupQueryDictionary(forKey: key)
        let status = SecItemDelete(qd as CFDictionary)
        
        if status != errSecSuccess {
            throw KeychainWrapperError.failure(status: status)
        }
    }
    
    private func setupQueryDictionary(forKey key: String) -> [String: Any] {
        var queryDictionary:[String: Any] = [kSecClass as String: kSecClassGenericPassword]
        
        queryDictionary[kSecAttrAccount as String] = key.data(using: .utf8)
        
        return queryDictionary
    }
    
}